" eBay may be in Luxembourg NOW, but they have PLENTY of other locations."
Yes, to trade in the EU they have plenty of other locations in the EU.
Companies wanting to do a lot of business in the EU need to have a legal presence in the EU. So upping sticks from Luxembourg isn't going to help them get round EU legislation.
If they have a choice between the problems of trying to do without that base and ensuring their traders are trading legally it'll be no contest.